Heart valve prosetheses are used in patients whose natural valves are damaged by conginital malformations or diseases and associated scarring and calcifications. Numerous heart valve designs have been developed using either a ball, leaflet or disc valving member. Each of these designs has certain advantages as well as deficiencies. They attempt, but do not achieve, the duplication of healthy natural heart valves. Problems of prosthetic heart valves are largely due to the shape and operating structure of the valves and the materials used in the valves.
Durability is a crucial factor in the clinical applicability of any heart valve, as a heart valve must open and close approximately forty million times a year. It is imperative that the material used in the heart valve be immune to biochemical degradation and mechanical failure due to wear and fatigue of rubbing or flexing of the components of the valve. Biodegration is interrelated with mechanical failure as it accelerates material fatigue and material breakdown. Rubbing and wear can accelerate the biochemical reaction, continually -exposing new surfaces to corroding media.
Leaf-type valves, as disclosed by Lord in U.S. Pat. No. 2,682,057 and Servelle in British Pat. No. 1,160,008, and disc-type valves as disclosed by Wada in U.S. Pat. No. 3,445,683; Schimert et al in U.S. Pat. No. 3,538,514 and Bokros in U.S. Pat. No. 3,546,711, have low pressure gradients and fair flow characteristics.
DeLaszlo, in U.S. Pat. No. 3,526,906, discloses prosthetic implants made from carbonaceous materials. The heart valve implant has a rigid base of carbon or graphite carrying a silicone rubber ball or a disc having legs of plastic material. Bokros, in U.S. Pat. No. 3,546,711, shows a carbon coated valve having a gate pivoted on a fixed pin. Cruz et al, in U.S. Pat. No. 3,367,364, and Kaster, in U.S. Pat. No. 3,467,143, disclose several pivoting disc heart valve designs. Shiley describes a pivoting disc heart valve in U.S. Pat. No. 3,698,018.
Nakib, in U.S. Pat. No. 3,438,394, discloses in FIGS. 8 and 9, a heart valve having a toroidal valving member that has a combined linear and angular movement as it opens and closes. Jordan, in U.S. Pat. No. 3,451,067, shows a heart valve having a check linearly guided on a rod. Similar valves are disclosed in U.S. Pat. Nos. 3,503,079; 3,601,877 and 3,812,542 as well as British Pat. No. 1,016,811. These valves, except the valves of Kaster and Shiley, are not pivoting disc valves. The base and disc pivoting structures of these valves are not adapted to be made entirely of rigid carbon materials. Parts of either the base or the pivoting structure must be movable or flexible to permit assembly of the disc into the base.
The natural heart valve has very little reverse flow of blood during the closing episode of the valve. The natural valve progressively closes in response to a drop in pressure of the blood flowing through the valve opening. Eddy currents on the distal side of the valve also effect the progressive closing of the valve. Artificial heart valves do not progressively close in response to a drop in the pressure of blood flowing through the valve passage.
Clinical use of pivoting disc valves wherein the valving member angularly moves to open and closed positions has shown that it is desirable to adjust the angular position of the valve after it has been implanted in the heart. The base of the valve is rotated relative to the suturing member secured to the heart tissue to orientate the valve member, as a pivoting disc, away from calcifications which can interfere with the free movement of the valving member. The valve is rotated with the handle or holder used to position the valve during the implant procedure. In order to permit angular orientation of the valve after it has been implanted, the suturing member has a loose fit on the valve base. This loose relationship between the suturing member and base is undesirable as the valve may shift in use and move or slide relative to the suturing member.